It is known that, during rollout on a landing runway following a landing (or following a decision to interrupt a takeoff), the deceleration (or the braking) of an aircraft is carried out either manually and directly by the pilot using the brake pedals, or by way of an automatic braking system which servo-controls a fixed deceleration predetermined by the pilot before landing, via a push-button or an electro-magnetized rotary button.
However, these braking systems, be they manual or automatic, have no awareness of the topographic reality of the landing runway (length, width, etc.) on which the landing is carried out.
Documents FR-2 817 979 and FR-2 857 468 disclose devices for automatically controlling the deceleration of an aircraft in the rollout phase which make it possible to partly remedy this drawback. These known devices in fact allow the crew of the aircraft to select an exit linkway on the landing runway and to manage automatically and optimally (aid to the selecting of a realistic exit linkway compatible with the known landing performance, minimization of the runway occupancy time, minimization of the necessary braking energy, improvement of comfort) the deceleration of the aircraft during rollout on landing until the selected exit linkway is reached. Consequently, under normal operational conditions, these customary devices guarantee that this exit linkway is reached in an optimal manner.
Moreover, document FR-2 897 593 discloses a method and a system for providing, during a landing, from before the aircraft contacts the landing runway, information about whether the landing will or will not be long, thus leaving time (if appropriate) to effect measures making it possible to remedy the drawbacks of a long landing. Accordingly, the altitude of the aircraft is measured, the horizontal distance separating said aircraft from the proximal end threshold of the landing runway is calculated, and an estimated finishing position of said aircraft on said landing runway is determined on the basis of this altitude and of this horizontal distance, as well as on the basis of an approach angle.
Furthermore, document US-2004/0167685 provides for the calculation of a critical point on the landing runway, beyond which the landing may lead to an overshoot of the runway, and for the emission of an alarm if the current descent axis of the aircraft reaches the runway beyond this critical point.
The object of the present invention is, more particularly, to forewarn the crew of the aircraft against a risk of longitudinal excursion from the landing runway, during rollout on this runway when landing.
It is known that, during a landing, a problem may appear as regards the normality of the landing conditions and their management by the crew of the aircraft. Indeed, before undertaking a flight, the crew must ensure that the landing of the aircraft on the destination airport is possible, that is to say that the scheduled landing performance, allied with expected exogenous conditions (meteorology, knowledge of the destination airport, experience of the crew, etc.) is compatible with the length of the landing runway available at said destination airport.
Nevertheless, it is possible that the meteorological conditions may deteriorate at the moment of the execution of the landing (appearance of strong precipitation, strong wind gradients, etc.) thus making it difficult for the crew to effect the landing right until the aircraft stops on the available length of the landing runway used (or else to obtain a speed which is compatible with the taking of an exit linkway that the aircraft expects to follow). Under such conditions, a risk of longitudinal runway excursion may become significant.
Now, this risk of runway excursion is currently fully managed by the crew, without any assistance, or any automated facility, by virtue of their experience, their training and good preliminary preparation for the flight, this not being satisfactory.